cfg80211: fix checking nl80211_send_station() return value

The return value from nl80211_send_station() is the length of the
skb, or a negative error, so abort sending the message only when
the return value was negative.

This fixes the ibss_rsn wpa_supplicant test case.

Reported-by: Jouni Malinen <j@w1.fi>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
diff --git a/net/wireless/nl80211.c b/net/wireless/nl80211.c
index 8e56eeb..c5661c5 100644
--- a/net/wireless/nl80211.c
+++ b/net/wireless/nl80211.c
@@ -11788,7 +11788,7 @@
 		return;
 
 	if (nl80211_send_station(msg, NL80211_CMD_DEL_STATION, 0, 0, 0,
-				 rdev, dev, mac_addr, sinfo)) {
+				 rdev, dev, mac_addr, sinfo) < 0) {
 		nlmsg_free(msg);
 		return;
 	}